The mechanism of action of several enzymes involved in vitamin B6 metabolism or dependent upon pyridoxal 5'-phosphate is being studied and compared. These include tryptophanase, D-serine dehydratase and pyridoxine dehydrogenase, all from microbial sources. The first two catalyze formally similar reactions that involve enzyme-bound alpha- aminoacrylate as an intermediate. The mechanism of decomposition of this complex, which seems to differ in the two enzymes, is being studied by borohydride reduction and other methods. Covalent modification studies are underway to attempt to implicate specific amino acid residues of the protein moiety as part of the active site. We are also comparing the mechanism of active uptake of (H3)- labeled vitamin B6 by various yeast and bacterial cells and hope to further characterize it. Metabolism and uptake of 5'-deoxypridoxine by animal and microbial tissues also is being studied by use of the tritiated compound. These projects are closely related to and not always well separated from those supported by a second USPHS grant, Nutrition and Metabolism of Microorganisms (AI 01575).